Electric Pump

ABSTRACT

A pump for pumping liquid has an electric motor driving an impeller disposed within a pump chamber. The motor has a stator, a rotor, and an end cap. The end cap has a printed circuit board upon which are mounted two brushes connected to a pair of motor terminals through a thermistor. Optionally, the motor may include, singularly or in combination, one or more inductors located between the brushes and the motor terminals, a varistor for preventing excessive voltage spikes electrically connected between the motor terminals, and one or more capacitors electrically connecting the motor terminals to ground.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201310215238.1, filed in The People's Republic of China on Jun. 3, 2013, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to an electric motor driven pump and in particular, to an electric pump having overcurrent protection.

BACKGROUND OF THE INVENTION

When an electric motor draws too much current, it may suffer damage from overheating.

One situation in which a motor may draw too much current is when its output is impeded. For instance, in an electric pump, the impeller may be blocked preventing the motor shaft from rotating, causing the motor to stall. In such a stall condition the motor may draw too much current and over heat.

For example, in an automotive application an electric pump may be used to spray water or a detergent solution on to the windshield or head lamps. In cold environments when the temperature drops below freezing, the water or detergent within the pump may freeze, preventing the impeller from rotating.

When the pump motor is powered on but the impeller is unable to move, the motor continues to draw power such that it generates a large amount of heat over a short period of time, potentially damaging the motor and creating a fire hazard. In order to solve this problem, a fuse can be located between the motor and its power source, and arranged to break if the motor exceeds a certain temperature. However, replacement of the fuse incurs additional maintenance costs, and can be a cumbersome process.

SUMMARY OF THE INVENTION

Accordingly, there exists a need for an electric pump which will not overheating when the impeller is unable to rotate. In addition, the electric pump may include electrical noise suppression components to prevent the pump from interfering with other electrical components and devices.

Accordingly, in one aspect thereof, the present invention provides an electric pump for pumping liquid, comprising: a pump housing defining a pump chamber; an impeller disposed in the pump chamber; and an electric motor for driving the impeller, the motor comprising: a stator defining a plurality of magnetic poles; and a rotor configured to rotate relative to the stator, the rotor comprising: a shaft; a rotor core fixed to the shaft; a commutator fixed to the shaft adjacent one end of the rotor core; and a plurality of winding coils wrapped around the rotor core and electrically connected to the commutator; first and second motor terminals configured to be connected to an external power source; first and second brushes in sliding contact with the commutator; and a positive temperature coefficient thermistor, wherein the first brush is electrically connected to the first motor terminal through the thermistor; and the second brush is electrically connected to the second motor terminal.

Preferably, the brushes, the thermistor, and the motor terminals are mounted on an end cap located on an axial end of the motor.

Preferably, the brushes and the thermistor are mounted on a printed circuit board mounted on the end cap of the motor.

Preferably, the pump includes a pump cover incorporating a connector housing accommodating the motor terminals, with a first end of the motor terminals disposed in the connector for connection to a power supply and a second end of the motor terminals being inserted in respective sockets disposed on the end cap.

Preferably, the pump has one or more inductors, respectively electrically connected between the brushes and the motor terminals.

Preferably, the one or more inductors comprise a first inductor and a second inductor, such that the first brush is connected to the thermistor through the first inductor, and the second brush is connected to the second motor terminal through the second inductor.

Preferably, a varistor is connected to the two motor terminals in series with the thermistor.

Preferably, a first capacitor connects a terminal of the thermistor not connected to the first motor terminal to ground, and a second capacitor connects the second motor terminal to ground.

Preferably, the capacitors are connected to a ground terminal that is connected to a motor housing of the motor.

Preferably, the pump is configured to pump water or a detergent solution onto an automobile windshield.

Preferred and/or optional features are set forth in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below.

FIG. 1A is a perspective view of an electric pump having a motor in accordance with the preferred embodiment of the present invention;

FIG. 1B is a sectional view of the pump of FIG. 1A;

FIGS. 2A and 2B illustrate an end cap assembly for the motor of FIG. 1A;

FIG. 3 illustrates a circuit board assembly used in the end cap assembly of FIGS. 2A and 2B;

FIG. 4 is a schematic diagram of the circuit board assembly of FIG. 3; and

FIG. 5 is a graph showing the electrical properties of a thermistor used in the motor of FIG. 1A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A and 1B illustrate an electric pump 10 used for pumping a liquid, in accordance with the preferred embodiment of the present invention. FIG. 1B is a longitudinal sectional view taken along the axis of the pump, which is coaxial with the axis of the motor. In this embodiment the liquid pump 10 is used in a vehicle to spray water, a detergent, or other type of liquid, onto a windshield. It is understood that in other embodiments, pump 10 may be used in any type of application that involves the pumping of a liquid.

Pump 10 comprises a motor 20, a pump chamber 11, and an impeller 14 connected to and driven by motor 20. The impeller is accommodated within the pump chamber. Pump chamber 11 has an inlet 52 connecting the pump chamber to a source of liquid (e.g., a water or detergent container) and at least one outlet 54 through which, in use, the liquid is discharged. During operation, motor 20 rotates impeller 14 creating a centrifugal force so that liquid flowing in from the inlet 52 is expelled through outlet 54. The pump chamber is defined by the space formed between a pump housing 12 and a pump plate 13.

In the embodiment shown in FIG. 1A, the pump has two outlets 54 interconnected by a diverter valve 17. In this embodiment, the direction of rotation of the impeller determines through which outlet the liquid will be pumped.

As shown in FIG. 1B, motor 20 comprises a stator 21, a rotor 22 rotatably mounted to stator 21, and an end cap assembly 30. Stator 21 comprises a motor housing 24 and a plurality of magnets 25 fixed to an inner wall of motor housing 24. Magnets 25 are permanent magnets, although it is understood that magnets 25 may comprise any type of component capable of generating a magnetic field and/or defining a magnetic pole, including electro-magnets. Preferably, motor housing 24 is substantially cylindrical. Most preferably, the motor housing is a deep drawn cup-shaped metal part having one open end and one closed end.

Rotor 22 comprises a shaft 26, a commutator 27 and a rotor core 28 attached to shaft 26, and a plurality of winding coils 29 wound around rotor core 28 and connected to commutator 27. One axial end of shaft 26 is rotatably attached to one end of motor housing 24, preferably the closed end by a bearing 23. The other axial end of shaft 26 is rotatably attached to end cap assembly 30 by another bearing 23. Bearings 12 may be ball bearings, bearing sleeves, or any other components that provide mechanical coupling between moving and stationary parts, allowing rotor 22 to rotate relative to stator 21.

Motor 20 is attached to pump plate 13 which forms a wall of pump chamber 11. Motor 20 and pump plate 13 are disposed inside pump housing 12 and a pump cover 60 closes the open end of the pump housing. Pump cover 60 is preferably splash proof to give motor 20 protection for the environment. Pump cover 60 has a mounting projection 64 and forms a connector 62 for connection a power supply to motor terminals A shaft seal 18 seals shaft 26 to pump plate 13. O-ring seal 19 seals pump plate 13 to pump housing 12 to provide a water tight pump chamber 11.

FIGS. 2A and 2B illustrate an end cap assembly 30 of the preferred embodiment. End cap assembly 30 comprises a plurality of brushes 31 arranged to make sliding contact with commutator 27. When motor 20 is powered, brushes 31 supply electrical power to winding coils 29 through commutator 27, causing rotor 22 to rotate within stator 21 and drive impeller 14.

End cap assembly 30 comprises an end cap 32 and a circuit board assembly 34 fixed to end cap 32. As illustrated in FIG. 3, brushes 31 are connected to circuit board assembly 34, and positioned on opposite sides of commutator 27, such that, when motor 20 is assembled, brushes 31 are able to maintain sliding contact with a surface of commutator 27. The illustrated brushes are of the leaf brush type, having a brush terminal 31 a fixed to the circuit board, a brush body 31 b arranged to make sliding contact with the commutator and connected to the brush terminal, electrically and mechanically, by a resilient brush arm 31 c. The brush body is of a carbon based material and the brush arm urges the brush body against the commutator. However, other types of brushes may be used.

Circuit board assembly 34 may comprise a printed circuit board (PCB) 36, and a plurality of electrical components, including a pair of motor terminals 38 a/b, a pair of chokes or inductors 40 a/b, a pair of sockets 42 a/b, a varistor 46, capacitors 50 a/b, and a positive temperature coefficient thermistor (PTC) 44. FIG. 5 is a graph illustrating the electrical properties of PTC 44 in accordance with the preferred embodiment.

In some embodiments, PCB 36 is configured such that some of the electrical components (e.g, inductors 40 a/b, and thermistor assembly 44) are arranged on one side of PCB 36, while the opposite side of PCB 36 carries a plurality of electrical traces connecting the electrical components in accordance with the circuit diagram illustrated in FIG. 4. Brushes 31, inductors 40 a and 40 b, sockets 42 a and 42 b, varistor 46 and PTC 44 are connected to PCB 36 by soldering.

Motor terminals 38 a/b are arranged to be connected to an external power source (not shown), such as a battery, generator, or outlet. Motor terminals 38 a/b connect to the electrical components on PCB 36 by being pressed into sockets 42 a/b. In the preferred embodiment, sockets 42 a/b are substantially U-shaped, each comprising a pair of clamping ends 43. At least one end of each pair of clamping ends 43 is substantially V-shaped and arranged such that a minimum gap between the ends of each pair of clamping ends 43 is smaller than a thickness of the motor terminals, allowing for motor terminals 38 a/b to be inserted into corresponding sockets 42 a/b and held in place by clamping ends 43. Preferably, both clamping ends of each pair of clamping ends are V-shaped and contact each other at the apex of the V in the relaxed state. As illustrated in FIG. 4, motor terminal 38 a is electrically connected to one of the bushes 31 through PTC 44 and inductor 40 a, while motor terminal 38 b is connected to the other brush 31 through inductor 40 b.

As illustrated in FIG. 3, PTC 44 comprises a thermistor element 44 b mounted between a pair of metal strips forming the thermistor terminals 44 a and 44 c. One thermistor terminal 44 c is connected to motor terminal 38 a and the other thermistor terminal 44 a is connected to inductor 40 a. This arrangement may be used to improve the physical strength of PTC 44. In addition, due to the mass of the thermistor terminals the temperature rise of the thermistor may be dampened slightly to allow the PTC to be less sensitive to sudden transient current surges.

During operation of motor 20, if rotation of impeller 14 is impeded (e.g., caused by freezing of liquid within pump chamber 11, the current flowing through motor 20 may rapidly increase, causing the temperature of thermistor 44 to rise. As illustrated in FIG. 5, after thermistor 44 exceeds a certain temperature, the resistance of thermistor 44 will increase significantly. The increased resistance of thermistor 44 reduces the amount of current that flows through motor 20, effectively turning the motor off, thus protecting motor 20 from suffering damage due to too much current draw. When the temperature of thermistor 44 decreases, its resistance will return to normal, allowing motor 20 to resume normal operation once impeller 14 is able to rotate again.

During normal operation of the pump, the current through the motor tends to fluctuate rapidly due to commutation by the commutator. This results in electrical noise being transferred to the power supply. Electrical noise is undesirable as it may interfere with other electrical products. In order to reduce the electrical noise created, inductors 40 are connected in series between brushes 31 and motor terminals 38, wherein the inductive properties of the inductors function to stabilize the current flow through winding coils 29. In the illustrated embodiment, each motor terminal 38 a/b is connected to a respective inductor 40 a/b.

To further enhance suppression of electrical noise, the motor terminals may be connected to earth via a capacitor 50 a/b. To this end, circuit board assembly 34 further comprises a ground terminal 48 to which one terminal of each of capacitors 50 a/b is connected. The other terminal is electrically connected to the terminals of inductors 40 a/b which are connected to motor terminals 38 a/b, respectively. In the preferred embodiment, ground terminal 48 is fixed to PCB 36 and connected to an edge of end cap 32, such that when end cap assembly 30 is assembled to motor housing 24, ground terminal 48 is connected to outer shell 24.

In the preferred embodiment, circuit board assembly 34 further comprises a varistor 46, wherein one terminal of varistor 46 is electrically connected to the terminal of inductor 40 a that is connected to motor terminal 38 a, while the other terminal of varistor 46 is electrically connected to the terminal of inductor 40 b that is connected to motor terminal 38 b. Varistor 46 exhibits a high resistance at low voltages, but a low resistance at high voltages. During operation, if the voltage across the motor terminals experiences a sudden fluctuation, e.g. a voltage spike caused by commutation, excess current caused by the spike in voltage can be shunted through the varistor, limiting the size of the voltage spike, thus further stabilizing the current drawn by motor 20.

It is understood that while the illustrated embodiments illustrate a motor 20 having an inner rotor design with rotor 22 accommodated and configured to rotate within stator 21, other configurations may be used in other embodiments, e.g., a brushless motor, or a motor having an outer rotor design with the stator being accommodated within the rotor. For example, in a brushless motor, inductors 40 a/b may be connected to one or more stator winding coils instead of electric brushes 31.

Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. For example, the ordering of or spatial relations among many of the described components may be changed. In addition, non-essential features may be omitted entirely or included in various combinations, not specifically described. The specification and drawings are, accordingly, to be regarded in an illustrative or explanatory rather than restrictive sense. Therefore, the scope of the invention is to be determined by reference to the claims that follow.

In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items. 

1. An electric pump for pumping liquid, comprising: a pump housing defining a pump chamber; an impeller disposed in the pump chamber; and an electric motor for driving the impeller, the motor comprising: a stator defining a plurality of magnetic poles; and a rotor configured to rotate relative to the stator, the rotor comprising: a shaft; a rotor core fixed to the shaft; a commutator fixed to the shaft adjacent one end of the rotor core; and a plurality of winding coils wrapped around the rotor core and electrically connected to the commutator; first and second motor terminals configured to be connected to an external power source; first and second brushes in sliding contact with the commutator; and a positive temperature coefficient thermistor, wherein the first brush is electrically connected to the first motor terminal through the thermistor; and the second brush is electrically connected to the second motor terminal.
 2. The pump of claim 1, wherein the brushes, the thermistor, and the motor terminals are mounted on an end cap located on an axial end of the motor.
 3. The pump of claim 2, wherein the brushes and the thermistor are mounted on a printed circuit board mounted on the end cap of the motor.
 4. The pump of claim 1, further comprising one or more inductors, electrically connected between the brushes and the motor terminals, respectively.
 5. The pump of claim 4, wherein the one or more inductors comprise a first inductor and a second inductor, such that the first brush is connected to the thermistor through the first inductor, and the second brush is connected to the second motor terminal through the second inductor.
 6. The pump of claim 1, further comprising a varistor, wherein the varistor is connected to the two motor terminals in series with the thermistor.
 7. The pump of claim 1, further comprising a first capacitor and a second capacitor, wherein the first capacitor connects a terminal of the thermistor not connected to the first motor terminal to ground, and the second capacitor connects the second motor terminal to ground.
 8. The pump of claim 7, wherein the capacitors are connected to a ground terminal that is connected to a motor housing of the motor.
 9. The pump of claim 1, wherein the pump is configured to pump water or a detergent solution onto an automobile windshield.
 10. The pump of claim 1, further comprising a pump cover incorporating a connector housing accommodating the motor terminals, with a first end of the motor terminals disposed in the connector for connection to a power supply and a second end of the motor terminals being inserted in respective sockets disposed on the end cap. 